Many downhole operations that are performed during the life of a well, such as during drilling, completing, stimulating, and/or producing, may utilize a downhole assembly that may be conveyed from a surface region to a desired, or target, region, or zone, of a wellbore conduit that forms a portion of the well. In wells that include a vertical, or at least substantially vertical, wellbore conduit, insertion and/or location of the downhole assembly within the desired region of the wellbore conduit may be accomplished by conveying the downhole assembly into the wellbore conduit under the influence of gravity. However, in wells that include deviated and/or horizontal wellbore conduits, or at least portions that are deviated and/or horizontal, a motive force other than gravity may need to be utilized to convey the downhole assembly to the target region of the wellbore conduit.
This motive force may be provided by inserting the downhole assembly into the wellbore conduit and providing a fluid to a portion of the wellbore conduit that is uphole from the downhole assembly, with the flow of the fluid into the wellbore conduit conveying the downhole assembly toward a terminal end of a wellbore that defines the wellbore conduit. This process may be referred to herein as pumping the downhole assembly into the wellbore, or as a pump-down operation.
During a pump-down operation, drag forces between the fluid that is flowing in the wellbore conduit and the downhole assembly generate a pressure drop across the downhole assembly, which provides the motive force to convey the downhole assembly within the wellbore. In general, a magnitude of this motive force, and thus a rate at which the downhole assembly is pumped into the wellbore, may be governed by a variety of factors, including a flow rate of the fluid and/or a cross-sectional area of the downhole assembly (or any suitable portion thereof) relative to a cross-sectional area of the wellbore conduit. Accordingly, downhole assemblies with a larger cross-sectional area may be conveyed more quickly and/or efficiently for a given fluid flow rate.
Fluid flow rates may be limited by other system components and/or fluid availability. Thus, a plug, or other large-diameter device, may be attached to a terminal end of the downhole assembly in order to provide a large cross-sectional area and efficient pumping down of the downhole assembly. Subsequent to the pump-down operation, the plug may be detached from the downhole assembly and may remain within the wellbore conduit, limiting and/or blocking fluid flow therepast. Typically, this plug must eventually be removed from the wellbore conduit, requiring associated time, equipment, labor, and expense.
Alternatively, an outer diameter of the downhole assembly, or a portion thereof, may be increased. However, increasing the outer diameter of the downhole assembly may limit other operations within the well. As an illustrative, non-exclusive example, and during stimulation and/or completion operations, it may be desirable to flow a sealing material, such as ball sealers, from the surface region, past the downhole assembly, and to a perforation that may be present in a wall of a conduit body that defines the wellbore conduit. The ability to flow such a sealing material past the downhole assembly may be limited by the outer diameter of the downhole assembly, thereby limiting a maximum outer diameter thereof. As another illustrative, non-exclusive example, and also during stimulation and/or completion operations, it may be desirable to flow the fluid, such as a fracturing fluid and/or a fluid that includes a proppant material, within the wellbore conduit and past the downhole assembly at a high flow rate, and the outer diameter of the downhole assembly may limit the flow rate that may be provided therepast. Thus, there exists a need for improved drag-enhancing structures that may be utilized during pump-down operations, as well as for systems and methods that include the improved drag-enhancing structures.